Methods and apparatus for sensing pressure

ABSTRACT

Methods and apparatus for sensing pressure in a hostile environment are described. In one example embodiment, a microwave radar based sensor is provided. The sensor is coupled to a signal conditioning unit. The signal conditioning unit includes at least one of a processor configured to determine a sensor value and a memory having pre-stored values therein, the pre-stored values representing possible sensor values. Each pre-stored value is assigned a respective pressure. The method includes operating the signal conditioning unit to sample a signal generated by the sensor, operating the signal conditioning unit to correlate a characteristic of the sampled signal to a pre-stored value having an assigned pressure, and operating the signal conditioning unit to generate a signal representative of the assigned pressure of the pre-stored value that is correlated to the sampled signal.

BACKGROUND OF THE INVENTION

This invention relates generally to engines and more particularly, tomethods and apparatus for sensing pressure in combustion cylinders ofreciprocating engines and combustion chambers of gas turbine engines.

Pressure within combustion cylinders and chambers of various types ofengines impacts operation of such engines. For example, gas turbineengines typically include a compressor section, a combustor section, andat least one turbine section. The compressor compresses air, which ismixed with fuel and channeled to the combustor. The mixture is thenignited to generate hot combustion gases. The combustion gases arechanneled to the turbine which extracts energy from the combustion gasesfor powering the compressor, as well as producing useful work to power aload such as an electrical generator or to propel an aircraft in flight.

Gas turbine engines operate in many different operating conditions, andcombustor performance facilitates engine operation over a wide range ofengine operating conditions. Controlling combustor performancefacilitates improving overall gas turbine engine operations.

The environment within combustion cylinders and combustion chambers isharsh, which limits the types of pressure sensors that can be used. Forexample, temperature within the cylinders of internal combustion enginescan reach over 1000° F. Known pressure sensors that utilizepiezo-electric and piezo-resistive elements have limited life withinsuch environment or require cooling, which increases the material andassembly costs for such engines.

Fiber optic based systems have been used in connection with sensingpressure in harsh environments. Producing reliable and robust sensorsbased on fiber optic materials, however, is challenging and has impactedwidespread use of such sensors.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect, a method for determining a pressure utilizing a microwaveradar based sensor is provided. The sensor is coupled to a signalconditioning unit. The signal conditioning unit includes at least one ofa processor configured to determine a sensor value and a memory havingpre-stored values therein, wherein the pre-stored values representingpossible sensor values. The method includes operating the signalconditioning unit to sample a signal generated by the sensor, operatingthe signal conditioning unit to correlate a characteristic of thesampled signal to a pre-stored value having an assigned pressure, andoperating the signal conditioning unit to generate a signalrepresentative of the assigned pressure of the pre-stored value that iscorrelated to the sampled signal.

In another aspect, a pressure sensor is provided. The sensor includes asensor body, a diaphragm mounted within the sensor body, and a channelextending from an open end of the sensor body to the diaphragm todirectly expose the diaphragm to a pressure. The sensor further includesa microwave radar sensing unit secured to the sensor body. The sensingunit includes a head positioned a distance from the diaphragm.

In yet another aspect, a gas turbine engine is provided. The engineincludes a compressor discharging a flow of air, and a combustorassembly positioned downstream from the compressor. The combustorincludes at least one combustion chamber. A turbine is positioneddownstream from the combustor. A pressure sensor is mounted to thecombustor. The sensor includes a sensor body, a diaphragm mounted withinthe sensor body, and a channel extending from an open end of the sensorbody to the diaphragm to directly expose the diaphragm to a pressure inthe combustion chamber. A microwave radar sensing unit is secured to thesensor body. The sensing unit includes a head positioned a distance fromthe diaphragm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary gas turbine engine.

FIG. 2 is a partial cross section view of a pressure sensor inaccordance with one embodiment of the present invention.

FIG. 3 is a schematic illustration of operation of the pressure sensorshown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is generally directed to a pressure sensor, andmethod of operating a pressure sensor, to generate a signalrepresentative of pressure in harsh environments, such as in thecombustion cylinder of a reciprocating engine and in a combustionchamber of a gas turbine engine. The present invention is describedbelow in reference to its application in connection with and operationof a gas turbine engine. However, it will be obvious to those skilled inthe art and guided by the teachings herein provided that the inventionis likewise applicable in many different types of combustion devicesincluding, without limitation, boilers, heaters and other turbineengines, and may be applied to systems consuming natural gas, fuel,coal, oil or any solid, liquid or gaseous fuel.

As used herein, references to “combustion” are to be understood to referto a chemical process wherein oxygen, e.g., air, combines with thecombustible elements of fuel, namely carbon, hydrogen and sulfur, at anelevated temperature sufficient to ignite the constituents.

FIG. 1 is a schematic illustration of an exemplary gas turbine engine 10including at least one compressor 12, a combustor assembly 14 and aturbine 16 connected serially. In the exemplary embodiment, compressor12 and turbine 16 are coupled by a shaft 18, which also couples turbine16 and a driven load 20. Engine 10 illustrated and described herein isexemplary only. Accordingly, engine 10 is not limited to the gas turbineengine shown in FIG. 1 and described herein, but rather, engine 10 maybe any suitable turbine engine.

In operation, air flows into engine 10 through compressor 12 and iscompressed. Compressed air is mixed with fuel to form an air/fuelmixture that is channeled to combustor assembly 14 where the air/fuelmixture is ignited. Combustion products or gases from combustor assembly14 drive rotating turbine 16 about shaft 18 and exits gas turbine engine10 through an exhaust nozzle 22.

FIG. 2 is a partial cross section view of a pressure sensor 30 inaccordance with one embodiment of the present invention. Sensor 30includes a sensor body 32 having a diaphragm 34 mounted therein. In oneembodiment, high temperature metal alloys, such as, but not limited to,Inconel® and/or Hastelloy®, are used in fabricating body 32 and/ordiaphragm 34. Diaphragm 34 is exposed to pressure environment via achannel 36 within sensor body 32. A threaded portion 38 of body 32 isprovided to secure sensor 30 to, for example, a combustion chamber of agas turbine engine. A microwave radar sensing unit 40 is secured tosensor body 32. Microwave radar sensing units are well known and arecommercially available, for example, from Radatec, Incorporated ofAtlanta Ga.

In the embodiment illustrated in FIG. 2, sensing unit 40 includesexternal threads 42 that mate with internal threads 44 of sensor body32. Sensing unit 40 includes a head 46 positioned at a selected distancefrom diaphragm 34, and an interface cable 48 is coupled to radar sensorhead 46 and, as described below, extends to a signal conditioning unit(not shown in FIG. 2).

Generally, sensor 30 is mounted to a gas turbine engine so thatdiaphragm 34 is directly exposed to the pressure within an enginecombustion chamber. External threads 38, for example, mate with threadsof an opening in the chamber. The relative location of sensor 30 willvary depending on the application and design.

FIG. 3 is a schematic illustration demonstrating operation of sensor 30.As shown in FIG. 3, sensor 30 is coupled to a signal conditioning unit50. In the example embodiment, unit 50 is processor based and includes amicroprocessor and a memory. Unit 50 is configured to sample the signalgenerated by sensor 30 and to store the signal in the unit memory. In analternative embodiment, the microprocessor includes an algorithm used todetermine an output based on input values, rather than, or in additionto, the use of a look-up table of values.

More particularly, and prior to normal operations, when the engine isnot operating, sensing unit 50 is operated so that a zero pressure (orambient pressure) reading is obtained from sensor 30. The magnitude ofthe signal from sensor 30 (which is representative of the distancebetween diaphragm and sensor head) at zero pressure is stored in signalconditioning unit 50. The engine is then operated at known combustionchamber pressures and sensor signals are obtained by signal conditioningunit 50 under such known pressures. Specifically, under known operatingconditions, diaphragm 34 deflects in a linear manner when exposed toatmospheres of varying pressure. The degree of the linearity ofdiaphragm 34 contributes to the accuracy of sensor 30. The output ofmicrowave radar sensor 30 is in proportion to the distance betweensensor head 46 and a surface of diaphragm 34. In the exemplaryembodiment, sensor 30 is calibrated using known pressures in thefactory. Alternatively, and particularly if variation due to theenvironment cannot be replicated in the factory, sensor 30 may becalibrated on engines or combustors in the field, wherein at knownoperating pressures, the sensor unit signal is stored (e.g., themagnitude of the sensor signal) and correlated to the known pressure.

During engine operation, signal conditioning unit 50 is operated tosample the signal generated by sensor 30. Signal conditioning unit 50 isalso operated to correlate a characteristic of the sampled signal to thepre-stored values having assigned pressures. Specifically, the magnitude(or some other characteristic) of the sensor signal is determined andmatched to the determined magnitude to the pre-stored values. Signalconditioning unit 50 is further operated to generate a signalrepresentative of the assigned pressure of the pre-stored value that iscorrelated to the sampled signal. This generated signal may be used, forexample, to display the assigned pressure to an operator and/or tocontrol engine operations.

In this manner, during operations of the gas turbine, both static anddynamic pressure values can be determined. The bandwidth of the pressuremeasurement is determined by the bandwidth of the microwave radar sensorand the diaphragm.

Similar, if not identical, sensor configurations and calibration can beperformed in order to use sensor in connection with other types ofengines. The sensor and sensor operation are not limited to the specificembodiments described herein.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A method for determining a pressure utilizing a microwave radar based sensor coupled to a signal conditioning unit, the signal conditioning unit including at least one of a processor configured to determine a sensor value and a memory having pre-stored values therein, the pre-stored values representing possible sensor values, each pre-stored value being assigned a respective pressure, said method comprising: operating the signal conditioning unit to sample a signal generated by the sensor; operating the signal conditioning unit to correlate a characteristic of the sampled signal to a pre-stored value having an assigned pressure; operating the signal conditioning unit to generate a signal representative of the assigned pressure of the pre-stored value that is correlated to the sampled signal; and transmitting the signal representative of the assigned pressure to a control mechanism.
 2. A method in accordance with claim 1 wherein the signal generated by the sensor is indicative of a deflection of a diaphragm exposed to the pressure being determined.
 3. A method in accordance with claim 1 wherein the diaphragm deflects linearly based on exposed pressure.
 4. A method in accordance with claim 1 wherein correlating a characteristic of the sampled signal to a pre-stored value comprises determining a magnitude of the sampled signal, and matching the determined magnitude to the pre-stored valued.
 5. A method in accordance with claim 1 wherein the pressure is the pressure of a combustion chamber of a gas turbine engine.
 6. A method in accordance with claim 1 wherein the pressure is the pressure of a combustion cylinder in a reciprocating engine.
 7. A pressure sensor, comprising: a sensor body; a diaphragm mounted within said sensor body; a channel extending from an open end of said sensor body to said diaphragm to directly expose said diaphragm to a pressure; and a microwave radar sensing unit secured to said sensor body, said sensing unit comprising a head positioned a distance from said diaphragm.
 8. A pressure sensor in accordance with claim 7 wherein said diaphragm is configured to deflect based on a pressure of gas in said channel.
 9. A pressure sensor in accordance with claim 8 wherein said diaphragm deflects linearly based on the gas pressure.
 10. A pressure sensor in accordance with claim 7 wherein said body further comprises a threaded portion to secure said sensor to an engine.
 11. A pressure sensor in accordance with claim 10 wherein the engine is a reciprocating engine.
 12. A pressure sensor in accordance with claim 10 wherein the engine is a gas turbine engine.
 13. A pressure sensor in accordance with claim 7 wherein said sensing unit comprises external threads that mate with internal threads of said sensor body.
 14. A pressure sensor in accordance with claim 7 further comprising an interface cable coupled to said radar sensor head. 